The invention concerns a ribbon cartridge for typewriters or similar office machines of the type including a ribbon arranged to be wound off a supply reel and rewound on a take-up reel and a casing having a bottom provided with a plurality of access openings for receiving elements sensing the end of the ribbon and the like.
Among the many known measures for damping the noise occurring in the vicinity of typewriters and similar printing machines, particular importance attaches to those devices through which the noise produced as the type element strikes the paper are shielded from the persons who are present in the vicinity of the machine. So-called acoustic enclosures, enclosing either the entire machine or being fitted only in the paper feed area above the platen, have proved to be especially effective. While with acoustic enclosures covering the entire machine it is possible to observe the text being typed through a sight window, access for insertion and alignment of the paper is extremely unwieldy. Therefore, acoustic enclosures of that type are not suited for offices involving frequent insertion of new sheets of stationery.
While with covers which are placed only on the paper feed and discharge in the area of the platen the paper handling is generally facilitated for the machine operator, a frequent consequence is that the noise damping cannot be accomplished with the desired effect. While with this type of acoustic covers the possibility of observing the printed text is generally satisfactory for the operator, a particular problem is the print head accessibility for changing the print wheel and the ribbon cartridge. Besides, acoustic hoods covering the platen are too expensive for low-cost correspondence typewriters. Additionally, if a machine, specifically an electric typewriter, is covered by an enclosure, a sound backup occurs within the enclosure and thus an increase of the noise level. The sound waves impinging from inside on the enclosure or flat components stimulate oscillable components to vibrations which, in turn, are the cause of the machine noise given off outwardly. For reduction of this sound backup, a ribbon cartridge has been suggested whose cup-shaped base component and cover are perforated. While the perforation reduces the sound back-up and the noise level inside the enclosure, the rub-off caused by the routing and the drive of the spent carbon ribbon drops through the holes in the bottom of the base component, soiling machine components which are located underneath. Such soiling is avoided with the ribbon cartridge according to the European patent disclosure No. 81 109 546.2 in that the sound absorption facilities of the base consist of depressions whose bottom is sealed by a membrane. Additionally, the bottom features collars surrounding the openings and additional bearing faces for the spools of the supply and take-up reels.
The problem underlying the invention is to provide a ribbon cartridge through which the sound backup inside the enclosure is effectively reduced and dropping of fines from the spent ribbon, through the openings in the base component of the cartridge casing, will be safely avoided. Additionally, the cartridge is to feature a compact design and enable a smooth drive of the supply and take-up reels, with the fines rubbing off the spent ribbon being kept low.